Jean-Luc Mélenchon gathered about 130000 people in Paris for a large gathering of "La France Insoumise."

Just as the French presidential race appeared to be settling into a comfortable two-person contest, with polls showing Marine Le Pen in a dead heat with Emmanuel Macron in the first round leading to a comfortable (and comforting) Macron victory in the second, the previously moribund left of the Left discovered that what Marx called “the old mole”—popular discontent well-concealed in its underground lair—still has some life left in it.

Jean-Luc Mélenchon, who had been languishing at around 12 or 13 percent in first-round estimates, well behind the front-runners at around 24 percent each, suddenly began rising. He is now at 18 or 19, even with or slightly ahead of the right-wing Republican candidate François Fillon and within striking distance of the front-runners, and thus with a slim but real chance of making it into the May 7 runoff.

Who is Jean-Luc Mélenchon and what accounts for his sudden surge? Born in Morocco in 1951, he first became involved in politics as a high-school student in May ’68. For most of his career he gravitated toward the left wing of the Socialist Party and in the early 2000s served as a junior minister (for vocational education) under Lionel Jospin. Socialist support for a new European Union constitutional treaty in 2005 drove Mélenchon farther toward the party’s left fringe, and in 2008 he concluded that the balance of power among the party’s factions had shifted too far to the right for him to remain a member. He therefore resigned and founded his own Left Party, modeled on Germany’s Die Linke. In the 2012 presidential election he ran in alliance with what remained of the French Communist Party as the candidate of the Left Front. Although pre-election polls showed him close to Marine Le Pen that year, he finished with only 11 percent to Le Pen’s 18.

This year he chose to run again but initially found himself tied for last place among the five top-tier candidates with Benoît Hamon, the surprise Socialist nominee, to whom Mélenchon had been close when both were members of the PS. Hamon, who defeated former prime minister Manuel Valls, the candidate of the party’s right wing, which Mélenchon had staunchly opposed, appealed to the same segment of the electorate as Mélenchon: voters hostile to any compromise with capitalism, suspicious of what they took to be the European Union’s embrace of neoliberalism, highly critical of the Hollande presidency (especially for tis liberalization of labor laws and subservient posture toward Germany), and unimpressed by the independent candidacy of Emmanuel Macron, who had served as minister of the economy under Hollande before launching the En Marche! movement, which is liberal on social issues and neoliberal on economic ones.

As long as both Hamon and Mélenchon remained in the race, drawing approximately equal number of voters from the same pool, there seemed to be no hope for the left of the Left to make it to the second round. But things began to change after the first presidential debate. Although Hamon had delivered, the day before, the speech of his life and one of the best political speeches I have ever heard, his performance in the debate was generally considered lackluster, while most observers agreed that Mélenchon, who is eloquent, erudite, and quick on his feet, beat all four of his top-tier rivals. In the next televised debate, which included not just the top five but all eleven of the candidates who qualified for the race by collecting at least 500 validated signatures of elected officials, Hamon was again passive while Mélenchon turned in a stunning performance, including a memorable exchange in which he caught Marine Le Pen flat-footed on the question of permitting conspicuous religious symbols in public spaces. Le Pen opposes Muslim veils but favors allowing Nativity scenes in city halls on the grounds that these are not religious symbols but simply manifestations of French “tradition.” Mélenchon deftly skewered the flagrant contradiction.

From that point on, his rise has been rapid, and Hamon’s symmetrical fall has been equally precipitous. This shift in voter sentiment has destabilized the race. Macron, who had appeared to be the inevitable choice of voters for whom stopping Le Pen was priority number one, no longer seems inevitable. Some on the left were finding it difficult to vote for Macron. His insistence that he was “neither left nor right” but would take the best ideas from both sides struck many as equivocal if not downright hypocritical. His debate performances seemed somewhat rote and bloodless, while Mélenchon displayed considerable verbal agility. Whereas his fiery invective had alienated voters in 2012, this year he seemed calmer, more mature, and prepared to pose as a sage offering lessons to his less experienced rivals.

Mélenchon is the candidate of leftist nostalgia. He is sympathetic to Russia, arguing that the West has pushed Putin into a more aggressive stance by threatening Russia’s near abroad. He has nothing but good to say about Third-World dictators such as Castro and Chavez. He attacks the EU as an agent of neoliberalism and threatens, as does Le Pen, to withdraw France’s membership unless the treaties are revised in ways to which other members will never all agree (and unanimous consent is required). He will impose a 100 percent income tax on anyone earning over 400,000 euros per year, despite the fact that France’s Constitutional Council ruled Hollande’s 75 percent tax on individuals earning more than one million euros unconstitutional. And he will abolish the Fifth Republic (he says without specifying how), diminishing the importance of the office for which he is running and returning power to the legislature.

Yet despite the unrealism of his program, Mélenchon’s newfound supporters find him more persuasive than Hamon, who foresees a future of zero economic growth and diminished need for work, with the state providing a minimum basic income to those left without jobs. Compared with this utopia, Mélenchon’s nostalgic socialism might seem familiar and perhaps even feasible if the stars were to align correctly (which they won’t, since even if he were to win the presidency, his chances of putting together a legislative majority are nil).

Mélenchon’s surge has called into question the few certitudes that remain in this year of extraordinary political upheaval in France. The early favorites—Juppé, Sarkozy, and Valls—were eliminated in the primaries (which undoubtedly has the parties, or what is left of them, rethinking the wisdom of primaries). The seemingly unstoppable upstart, Macron, has slipped slightly in the polls and seems to have run out of reserves from which he can draw new first-round support. He has captured the soft left—Valls threw his support to Macron several weeks ago (a mixed blessing from Macron’s point of view), the center (François Bayrou chose not to run against him), and much of the Juppéist right. But he cannot seem to crack what remains of the marxisant left, and if Mélenchon succeeds in stealing still more votes from Hamon’s base, he could make it to the second round.

At this point, one can envision a second round pitting any two of the top four candidates against each other. And make no mistake: a Mélenchon-Le Pen face-off would come as a thunderclap from Olympus, a sign that, as Raymond Aron put it four decades ago, “Ce peuple est encore dangéreux.” One might have thought that the French had overcome their romantic attachment to revolution, to the idea that the slate of the past can be wiped clean and everything started anew, but there is an outside chance that the old mole is even now grubbing its way somewhere close to the surface and will spring forth on the night of Sunday, April 23. For some this is a sign of hope, for others an occasion for mounting fear.